A mass spectrometry method is a technique that is widely used as a means for analyzing various substances in many technical fields. Given the great demand for mass spectrometry, ionization methods for ionizing samples are under development, thus increasing the applicability of mass spectrometry to various samples, and making it possible to analyze a large variety of substances.
However, many conventional mass spectrometry methods require a special space (closed environment) for ionizing an analysis sample under conditions such as a high temperature, a vacuum, a high voltage, laser irradiation, and the like. That is, in principle, it is necessary to seal a sample in a sealed ionization chamber and ionize the sample, and these methods place significant restrictions on performing sample analysis (see Non-Patent Documents 1 and 2, for example).
In such a situation, new technologies such as the DART method and the DESI method have been developed as ionization methods that can achieve real-time direct ionization of a sample under ambient conditions (see Non-Patent Documents 1 to 4, for example).
Here, the DART (direct analysis in real time) method is a method in which an interaction between molecules (particularly water molecules) in the atmosphere and a sample is induced by discharging excitation gas at the sample under the atmospheric environment to ionize the sample. The DART method is an excellent method with which the sample can be directly ionized merely by being held close to an ion source in an open system.
The DESI (desorption electrospray ionization) method is a method in which electrically charged minute droplets of a solvent for ionization are attached to the surface of a sample by spraying the solvent onto the surface of the sample using a capillary to which voltage is applied, and mass spectrometry is performed on the ionized sample desorbed from the surface of the sample at that time.
Although the DART method and the DESI method are excellent methods that enable atmospheric-pressure real-time mass spectrometry, there is a disadvantage in that these methods are unsuitable for analysis of a volatile substance in principle.
These methods are methods in which ionization is performed in an open system and thus there is an inherent fundamental problem that if a volatile substance is analyzed, the ionized sample is scattered by diffusion or the like because of the structure of an apparatus, resulting in a marked decrease in detection sensitivity.
As described above, with the mass spectrometry methods using an ion source of conventional technologies, there is no technique for analyzing a volatile substance with a high sensitivity in real time under ambient conditions.
As a technique of a conventional technology for improving the detection sensitivity of a volatile substance, the only means is to analyze a gaseous sample or the like collected in a collection bottle, a sampling bag, or the like during a certain period of time, and therefore, a technique for analyzing a volatile substance with a high sensitivity “in real time under ambient conditions” has been anticipated. Moreover, it is desired that this analysis can be realized with a simple operation.
It should be noted that there is a technique in which a volatile substance is analyzed by gas chromatography (GC method) as a mass spectrometry method that enables highly sensitive analysis, but it requires pretreatment of the sample and a long measurement time (specifically one hour or more), and thus real-time analysis is not possible.